178 Davis — Dana's Confirmation of 



Moreover, the structure of the reef should show cross-bedding 

 on a gigantic scale, for the reef advances on a foundation of its 

 own talus ; and in the inclined layers of the talus disordered 

 structures might be locally expected, as the result of submarine 

 "landslides," if they may be so called. During the outgrowth 

 of the reef its superficial parts will be more or less dissolved 

 away in the excavation of the lagoon ; hence if such a reef is 

 uplifted, so as to form a terrace around its mountain center, its 

 stratification will be inclined at a significantly steeper angle 

 than the slope of the foundation on which it is built ; while in 

 the case of a reef formed during subsidence a large part of the 

 reef may consist of horizontal strata. 



The first of these deduced consequences of the theory of out- 

 ward growth is rarely if ever confirmed by the facts. Existing 

 barrier reefs are not as a rule associated with alluvial plains 

 around the inner border of their lagoons. Delta-plains of mod- 

 erate extent often occupy the bay heads, but the very form of 

 the bays upon which they encroach shows that subsidence has 

 taken place ; and the small area of many delta-plains indicates 

 that the subsidence has occurred during the formation of the 

 barrier reef. Hence the theory of outward growth during a 

 still-stand of a central island is not acceptable as a means of 

 accounting for reefs of this class. The theory cannot be 

 accepted as explaining actual barrier reefs, unless by way of 

 exception, however reasonable it is and however easily it may 

 be conceived. 



The second deduced consequence of the theory of outward 

 growth appears to be seldom supported by the facts, for the 

 strata of uplifted reefs, as far as I have read, are usually hori- 

 zontal. This consequence may perhaps be supported in a few 

 cases, where uplifted reefs are described as possessing inclined 

 strata ; but the descriptions of these cases do not suffice to dis- 

 tinguish reefs of outward growth on a still-standing foundation, 

 where the whole reef should consist of inclined strata, from 

 reefs of upward growth during subsidence, where only the 

 peripheral strata should be inclined and the rest horizontal. In 

 several articles in which uplifted reefs are described, the atti- 

 tude of their stratification is not mentioned ; perhaps because 

 it could not be recognized ; perhaps because districts of recent 

 elevation have not often in-the past offered favorable conditions 

 for the development of thick reefs in which, after elevation, 

 the lines of structure could be easily detected. But the real 

 difficulty here seems to be rather that the observers of uplifted 

 reefs did not have the alternative theories of reef formation 

 and their contrasted consequences clearly in mind ; and the 

 records made by such observers are often wanting in critical 

 value. For example, on Eua island of the Tonga group, Lister 



